This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. Section 119 from an application for METHOD FOR DETECTING TRANMISSION RATE OF CODE DIVISION MULTIPLE ACCESS (CDMA) TYPE COMMUNICATION TERMINALS filed earlier in the Korean Industrial Property Office on the 10th day of Feb. 1999 and there duly assigned Serial No. 4611/1999.
1. Field of the Invention
The present invention relates to a wireless communication terminal employing a Code Division Multiple Access (CDMA) scheme, and more particularly to a method for rapidly detecting a transmission rate during the demodulating operation.
2. Description of the Related Art
In general, a wireless communication terminal employing Code Division Multiple Access (CDMA) scheme is adapted to transmit the compressed data according to a predetermined transmission rate. The predetermined transmission rate may be one of the following: 9.6 Kbps, 4.8 Kkbps, 2.4 Kbps, or 1.2 Kbps. The implementation of a paging channel allows the wireless communication terminal to know the specific transmission rate to be used so that the transmission rate does not need to be detected from the received data during the demodulation process. When a telephone call is made through the use of a traffic channel, the transmission rate is variable depending on the amount of voice data involved in the transmission. For example, when either the calling party or the called party is in a mute state, a transmission rate of 1.2 K is used. However, when either party produces sound, a transmission rate of 9.6 K is used. Accordingly, the demodulation process for the received signals always requires the knowledge of the transmission rate at which the data is to be transmitted.
Conventionally, the detection of a transmission rate requires that the received data to be decoded and the decoded data signal to be encoded again at one of the transmission rates, such as 9.6 kbps, 4.8 kbps, 2.4 kbps, and 1.2 kbps. Then, the encoded signal is compared with the originally received signal prior to the decoding process. Based on the comparison result, the received data is adapted to be demodulated at an optimal transmission rate. A continuous execution of the above operation for every frame (20 microsec) of the received data is required to detect the transmission rate. Accordingly, there have been some problems because the detection of the transmission rate requires a series of data processing operations, such as decoding, encoding and comparing operation. Thus, it takes a relatively long period of time to detect the transmission rate at which the data is to be transmitted. Moreover, when the transmission rate is diversified, the hardware component of the communication terminal is easily overloaded, and, in some cases, it may be impossible to communicate in real time. Furthermore, such a conventional transmission rate detection method may be unsuitable for future communication systems requiring more variety of transmission rates.
Therefore, the object of the present invention is to provide a method for rapidly detecting the transmission rate at which the data is to be transmitted during the demodulation operation of the received data signal in wireless communication terminals employing the Code Division Multiple Access (CDMA) scheme.
In accordance with one embodiment of the present invention, a method of detecting a transmission rate in a wireless communication terminal of a Code Division Multiple Access (CDMA) scheme includes the steps of:
decoding and encoding, at a selected transmission rate, a frame signal corresponding to a data frame currently being received by a de-interleaver from a modulator-demodulator (modem) in response to the reception of the data frame;
comparing the encoded frame signal with the current frame signal being received from the modulator-demodulator to determine whether there are errors in an amount less than a predetermined threshold value;
transmitting a signal indicative of the selected transmission rate to a vocoder if there are errors in an amount less than the predetermined threshold value and determining whether the reception of all data frames is completed;
returning to the encoding and decoding step if the reception of all data frames is not completed; and,
selecting another one of the transmission rates other than the previously selected transmission rate used to decode and encode if there are errors in an amount greater than the predetermined threshold value, then returning to the encoding and decoding step.
According to another embodiment of the present invention, a method of detecting a transmission rate in a wireless communication terminal of a Code Division Multiple Access (CDMA) scheme includes the steps of:
decoding and encoding, at each of a plurality of transmission rates, a frame signal corresponding to a data frame currently being received by a de-interleaver from a modulator-demodulator (modem) in response to the reception of the data frame;
comparing each of the encoded signals with the current frame signal received from the modulator-demodulator, respectively, and detecting a specific transmission rate generating the lowest error;
transmitting a signal indicative of the detected transmission rate having the lowest error to a vocoder and setting the detected transmission rate as a new transmission rate;
determining whether the reception of all data frames from the modulator-demodulator is complete;
if reception of all data frames is not complete, encoding and decoding, at the new transmission rate, a next frame signal corresponding to the data frame received from a modulator-demodulator via the de-interleaver;
comparing the encoded frame signal with the next frame signal received from the modulator-demodulator to determine whether there are errors in an amount less than a predetermined threshold value;
if there are errors in an amount less than the predetermined threshold value, transmitting a signal indicative of the set transmission rate to a vocoder and returning to receive the next frame signal; and,
if there are errors in an amount greater than the predetermined threshold value, returning to the first decoding and encoding step at each of a plurality of transmission rates.